1. Field of the Invention
The present invention is broadly concerned with light attenuating compounds for incorporation into photolithographic compositions (e.g., anti-reflective coatings and contact or via hole fill compositions) utilized in the manufacturing of microdevices. More particularly, the light attenuating compounds are non-aromatic and are especially useful for absorbing light at shorter wavelengths (e.g., 248 nm). The compounds can be physically incorporated into the particular composition, or alternately, can be chemically bonded to a polymer binder already present in the composition. The compounds of the invention comprise conjugated aliphatic and alicyclic moieties which meet the necessary light absorbency requirements for the composition while enhancing the plasma etch rate of the composition when compared to prior art aromatic dyes.
2. Description of the Prior Art
A frequent problem encountered by photoresists during the manufacturing of semiconductor devices is that activating radiation is reflected back into the photoresist by the substrate on which it is supported. Such reflectivity tends to cause blurred patterns which degrade the resolution of the photoresist. Degradation of the image in the processed photoresist is particularly problematic when the substrate is non-planar and/or highly reflective. One approach to address this problem is the incorporation of an anti-reflective dye either into the photoresist layer, into a contact or via hole fill composition, into a bottom anti-reflective coating (BARC), or as a separate layer adjacent the photoresist layer.
Prior art BARC compositions usually contain aromatic anti-reflective dyes which attenuate light that would otherwise reflect from the substrate during photoresist exposure. For example, anthracene and naphthalene derivatives are typically the preferred dyes for use at 248 nm exposing wavelengths. Dyes comprising a benzene ring with at least one conjugated substituent are widely used in BARC's which operate at 365 nm, while dyes comprising a benzene ring without conjugated substituents have ample absorptivity to satisfy most 193 nm applications.
Aromatic dyes have been preferred for BARC applications because of their high light absorbency per unit mass as well as their wide availability, easy preparation, and high chemical stability. While aromatic dyes are useful for achieving high film optical density, they limit the plasma etch rate of the BARC compositions by virtue of their chemical stability. Aromatic dyes require considerably more energy for decomposition than do the polymer binders (which are typically non-aromatic) used in the BARC compositions. As a result, the composite etch rate is highly dependent on the aromatic character of the dyes.
U.S. Pat. No. 4,719,166 to Blevins et al. discloses the use of certain butadienyl dyes in a photoresist layer, an anti-reflective layer, or a planarizing layer for protecting photoresist elements against reflection of activating radiation from the substrate. However, the dyes of the '166 patent are not attached to the backbone of a polymer binder, thus permitting them to readily solubilize in the photoresist, often leading to pattern degradation. Furthermore, current technology continues to require increasingly complex circuitry be imprinted on chips of decreasing size. These smaller chips require shorter wavelengths (e.g., 248 nm) be used during photoresist exposure. The dyes of the '166 patent are useful for absorbing light only at 365 nm exposure wavelengths, making them unsuitable for use in the manufacturing of most current microdevices.
There is a need for a compound which can effectively attenuate light at shorter wavelengths and which does not inhibit the etch rate of the particular BARC or contact or via hole fill composition in which it is utilized.